Background: Hypoglycaemic disorders are rare in patients without Diabetes Mellitus but  may  have  a  variety  of  causes  including  endogenous  hyperinsulinaemia  (EH). A mixed  meal  test  (MMT)  has  been proposed  as  a  useful  method  to  confirm  the presence of a postprandial hypoglycaemic disorder. However, there are currently no consensus guidelines for interpreting the MMT.

Method:   We  studied  fifty  patients  who  underwent  MMT  at  our  hospital  between 2008-2016. Patients ingested a standardised breakfast of approximately 1700kJ (48% carbohydrate,  33%  fat,  17%  protein,  2%  other  nutrients)  after  an  overnight  fast. Venous  samples  for  the  measurement  of  glucose  (BG), C-peptide  and  insulin  were collected  prior  to  eating,  then  every  30  min  for  five  hours.  A  result  was  considered positive  if   venous  BG  was ≤3.0 mM  with  the  patient  experiencing   symptoms consistent  with  hypoglycaemia. We reviewed the  indication  for  testing,  the  final clinical diagnosis and analysed the glucose and insulin responses to a MMT. We also calculated the Homeostasis Model Assessment (HOMA) score and Matsuda Index (a measure of insulin sensitivity after a glucose load) (1). Results: There were multiple indications   for   performing   a   MMT,   with   the predominant indication being suspicion of EH in otherwise healthy individuals. Three of thirty-six (8.3%) patients who were previously well and referred for suspected EHdeveloped hypoglycaemic during the test. In  patients  who developed hypoglycaemia, those  that  were  otherwise  well  had  the  highest  MATSUDA  indices, insulin and C-peptide levels, and lower HOMA scores. 

Conclusion: We observed different indices of insulin sensitivity according to the underlying cause of postprandial hypoglycaemia.  The MMT may be  helpful  for  investigating  the presence of a range of post-prandial hypoglycaemic disorders.